Abstract
Sixteen Ni-base alloys composed of 10〜25wt%, Cr, 0〜15wt% Mo with Cr and Mo varying at increments of 5wt%, and Ni(60〜90wt%)were prepared by melting under a high-purity argon atmosphere and subsequent centrifugal casting.Tensile strength, elongation, Vickers hardness and resistance to tarnishing were measured.Orthogonal analysis of variance was made on the amounts of Cr and Mo, and an orthogonal polynomial function was determined to estimate the optimum composition of crown and bridge casting alloys.The tensile strength of the castings increased with Mo content, but decreased at 15wt% Mo and 25wt% Cr.Alloys with a tensile strength of 65kgf/mm2 or more were in the range of 15 to 22wt% Cr and 12 to 15wt% Mo.The elongation of the castings showed a maximum value of about 27% with alloys of 17wt% Cr and 11wt% Mo.Vickers herdness increased with Cr and Mo content, reaching 218 at 25wt% Cr and 15wt% Mo.The brightness L* after 3 days of immersion in a 1% lactic acid0.1% sodium sulfide mixed solution at 37℃ increased with Cr and Mo content when Cr content of an alloy 15wt% or more, and an improvement in resistance to tarnishing was noted.The alloy containing 69wt% Ni-18wt% Cr-13wt% Mo appeared to have a maximum tensile strength, allowances being ±2 and ±1wt% for Cr and Mo, respectively.Tensile strength, elongation, Vickers hardness and brightness L* of this alloy were 67±4kgf/mm2, 25±5%, 188±4 and 71±1, respectively.
